private static Implication RemoveNotDistinctLiteral(Implication rule, Negation notDistinctLiteral)
{
//Figure out the substitution we want...
//If we have two constantsin Either Remove one or
//maybe get rid of the ___?
//One is a variablein Replace the variable with the other thing
//throughout the rule
var distinct = (Fact)notDistinctLiteral.Negated;
Term arg1 = distinct.GetTerm(0);
Term arg2 = distinct.GetTerm(1);
if (arg1 == arg2)
{
//Just Remove that literal
var newBody = new List<Expression>();
newBody.AddRange(rule.Antecedents.Conjuncts);
newBody.Remove(notDistinctLiteral);
return new Implication(rule.Consequent, newBody.ToArray());
}
var p1 = arg1 as TermVariable;
if (p1 != null)
{
//What we return will still have the not-distinct literal,
//but it will get replaced in the next pass.
//(Even if we have two variables, they will be equal next time through.)
var sub = new Substitution();
sub.AddMapping(p1, arg2);
return (Implication)rule.ApplySubstitution(sub);
}
var variable = arg2 as TermVariable;
if (variable != null)
{
var sub = new Substitution();
sub.AddMapping(variable, arg1);
return (Implication)rule.ApplySubstitution(sub);
}
if (arg1 is TermObject || arg2 is TermObject)
{
//We have two non-equal constants, or a constant and a function.
//The rule should have no effect.
return null;
}
//We have two functions. Complicated! (Have to replace them with unified version.)
//We pass on this case for now.
//TODO: Implement correctly.
throw new Exception("We can't currently handle (not (distinct <function> <function>)).");
}
public override bool Mgu(Term t, Substitution subsSoFar)
{
if (t is TermObject)
{
Term replacement = subsSoFar.GetMapping(this);
if (replacement != null)
{
TermVariable termVariable = replacement as TermVariable;
if (termVariable != null)
{
subsSoFar.AddMapping(this, t);
subsSoFar.AddMapping(termVariable, t);
return true;
}
return replacement.Equals(t);
}
// There was no replacement:
// Add a mapping for the variable to this term-object
subsSoFar.AddMapping(this, t);
return true;
}
var variable = t as TermVariable;
if (variable != null)
{
TermVariable it = variable;
Term myReplacement = subsSoFar.GetMapping(this);
Term itsReplacement = subsSoFar.GetMapping(it);
if (itsReplacement == null)
{
// just map 'it' to me (or my replacement)
if (myReplacement == null)
{
if (!Equals(it))
subsSoFar.AddMapping(it, this);
}
else
{
if (!(myReplacement is TermVariable) || !myReplacement.Equals(it))
subsSoFar.AddMapping(it, myReplacement);
}
return true;
}
// At this point, 'it' has a replacement.
if (myReplacement == null)
{
// I don't have a replacement, so map me to it, or to its replacement
if (!(itsReplacement is TermVariable) || !itsReplacement.Equals(this))
subsSoFar.AddMapping(this, itsReplacement);
return true;
}
// At this point, both term variables have replacements.
// So make sure that they are the same!
return myReplacement.Equals(itsReplacement);
}
var func = t as TermFunction;
if (func != null)
{
Term myReplacement = subsSoFar.GetMapping(this);
// Case 1: I have a replacement
if (myReplacement != null)
// See if my replacement can be unified with the function
return myReplacement.Mgu(func, subsSoFar);
// Case 2: I have no replacement
TermFunction itsReplacement = subsSoFar.GetMapping(func);
if (itsReplacement.HasVariable(this))
return false;
// just set my replacement to the function
subsSoFar.AddMapping(this, itsReplacement);
return true;
}
throw new Exception("TermVariable.mgu: Don't know how to handle term of type " + t.GetType().Name);
}